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Canada skyburst blamed on 10-ton rock

Nov. 28, 2008
Courtesy University of Calgary
and World Science staff

An in­ves­ti­ga­t­ion of a fire­ball that lit up the skies of west­ern Can­a­da on Nov. 20 has con­clud­ed that it was caused by a roughly 10-ton as­ter­oid frag­ment plow­ing in­to the at­mos­phere. 

Pieces of the the desk-sized space rock should be dis­cov­er­a­ble in part of west­ern Sas­katch­e­wan, said Al­an Hil­de­brand of the Uni­ver­s­ity of Cal­ga­ry, one of the re­search­ers. Hil­de­brand and a grad­u­ate stu­dent re­ported find­ing sev­er­al frag­ments late Thurs­day near the Al­ber­ta-Sas­katch­e­wan bor­der.

Frame from an ama­teur vi­deo of the ex­plo­sion (cour­tesy Can­west News Ser­vice)
The in­ves­ti­ga­tors said the fire­ball first ap­peared about 80 km (50 miles) above and just east of the city of Lloy­d­min­ster, at the bor­der of Al­ber­ta and Sas­katch­e­wan, and trav­eled south-south­east to­wards the Bat­tle Riv­er val­ley, frag­menting spec­tac­u­larly in a se­ries of ex­plo­sions.

The rock hit the at­mos­phere at a steep an­gle of about 60 de­grees from hor­i­zon­tal at 5:26 p.m. lo­cal time and lasted about five sec­onds, the re­search­ers said. The fire­ball was recorded on all-sky and se­cur­ity cam­er­as scat­tered across Sas­katch­e­wan and Al­ber­ta in ad­di­tion to be­ing wit­nessed by tens of thou­sands of peo­ple who saw it streak across the sky, saw its blue flash, or heard the sub­se­quent ex­plo­sions.

“The pub­lic re­sponse to this fire­ball has been the larg­est that we have ev­er had in Can­a­da,” said Hil­de­brand, Can­a­da Re­search Chair in Plan­e­tary Sci­ence and Co­or­di­na­tor of the Ca­na­di­an Fire­ball Re­port­ing Cen­tre at the Uni­ver­s­ity of Cal­ga­ry. 

Hil­de­brand said the fire­ball was like a billion-watt light­bulb shin­ing in the sky, turn­ing night in­to day with a blu­ish white light. It il­lu­mi­nated the ground for sev­er­al hun­dred kilo­me­ters in all di­rec­tions in­clud­ing as far south as Vaux­hall, Al­ber­ta.

“Thanks to ev­eryone’s help we are now be­gin­ning to de­lin­e­ate the tra­jec­to­ry of the fire­ball, so that its pre­fall or­bit can be de­ter­mined. We have al­so out­lined an ar­ea where its me­te­orites may have fal­l­en,” Hil­de­brand added.

The weight es­ti­mate for the ob­ject is de­rived from an en­er­gy es­ti­mate cal­cu­lat­ed in turn from in­fra­sound records by Pe­ter Brown, a me­te­or phys­icist at the Uni­ver­s­ity of West­ern On­tar­io. In­fra­sound is very deep sound, too low to be aud­ible by hu­mans, pro­duced by ex­plo­sions that can trav­el thou­sands of kilo­me­ters.

“At least half a doz­en in­fra­sound sta­t­ions rang­ing from Green­land to Utah, in­clud­ing Can­a­da’s Lac Du Bon­nett, Man­i­to­ba and El­gin Field, On­tar­i­o sta­t­ions, recorded en­er­gy from the fire­ball’s ex­plo­sions. The in­di­cat­ed en­er­gy is ap­prox­i­mately one third of a kil­o­ton of TNT,” Brown said.

Brown al­so said that a fire­ball this size only oc­curs over Can­a­da once ev­ery five years on av­er­age. About ten fire­balls of this size oc­cur some­where over the Earth each year. Lefto­ver frag­ments from the Nov. 20 event should be ly­ing with­in Sas­katch­e­wan’s Man­i­tou Lake Ru­ral Mu­nic­i­pal­ity north of Mars­den and Neil­burg, and just south of the Bat­tle Riv­er in an ar­ea that is mostly cleared for cul­tiva­t­ion, re­search­ers added.

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An investigation of a fireball that lit up the skies of western Canada on Nov. 20 has concluded that it was caused by a roughly 10-ton asteroid fragment plowing into the atmosphere. Chunks of the the desk-sized space rock should be discoverable in part of western Saskatchewan, said Alan Hildebrand of the University of Calgary, one of the researchers. Hildebrand and a graduate student reported finding several fragments late Thursday near the Alberta-Saskatchewan border. The investigators said the fireball first appeared about 80 km (50 miles) above and just east of the city of Lloydminster, at the border of Alberta and Saskatchewan, and traveled south-southeast towards the Battle River valley, fragmenting spectacularly in a series of explosions. The fireball hit the atmosphere at a steep angle of about 60 degrees from horizontal at 5:26 p.m. local time and lasted about five seconds, the researchers said. The fireball was recorded on all-sky and security cameras scattered across Saskatchewan and Alberta in addition to being witnessed by tens of thousands of people who saw it streak across the sky, saw its blue flash, or heard the subsequent explosions. “The public response to this fireball has been the largest that we have ever had in Canada,” said Hildebrand, Canada Research Chair in Planetary Science and Coordinator of the Canadian Fireball Reporting Centre at the University of Calgary. Hildebrand said the fireball was like a billion-watt lightbulb shining in the sky, turning night into day with a bluish white light. It illuminated the ground for several hundred kilometers in all directions including as far south as Vauxhall, Alberta. “Thanks to everyone’s help we are now beginning to delineate the trajectory of the fireball, so that its prefall orbit can be determined. We have also outlined an area where its meteorites may have fallen,” Hildebrand added. The weight estimate for the object is derived from an energy estimate calculated in turn from infrasound records by Peter Brown, Canada Research Chair in Meteor Physics at the University of Western Ontario. Infrasound is very low frequency sound produced by explosions that can travel thousands of kilometers. “At least half a dozen infrasound stations ranging from Greenland to Utah, including Canada’s Lac Du Bonnett, Manitoba and Elgin Field, Ontario stations, recorded energy from the fireball’s explosions. The indicated energy is approximately one third of a kiloton of TNT,” Brown said. Brown also said that a fireball this size only occurs over Canada once every five years on average. About ten fireballs of this size occur somewhere over the Earth each year. Leftover fragments from the Nov. 20 event should be lying within Saskatchewan’s Manitou Lake Rural Municipality north of Marsden and Neilburg, and just south of the Battle River in an area that is mostly cleared for cultivation, researchers added.